SEA-URCHINS AND SEA-CUCOIBERS. 331 



Dili}- repeat the conjecture wliicli I liave hazarded in 

 the case of the Polyzoan " birds' heads," viz., that the 

 PedlctllaHcs are intended to seize minute animals, and 

 to hold them till they die and decompose, as baits to 

 attract clouds of Infusoria, which, multiplying in the 

 vicintiy or the Urchin, may afford it an abundant sup- 

 ply of food 



There is ^'ct another series of organs which stretch 

 out from every part of the periphery of this living box ; 

 scarcely less numerous than either the spines or Pedi- 

 cellarioe, but very different from both. They are what 

 I alluded to juct now as the feet. Let us pay a mo- 

 ment's attention to their appearance and action, before 

 we examine theix- structure. 



"We see, then, extending from various points of the 

 shelly case of the Urchin, and reaching to twice or 

 thrice the length of the longest spines, slender pellucid 

 tubes, slightly tapering towards tlieir free extremity, 

 which then abruptly dilates into a hemispherical knob, 

 with a flat end. These very delicate organs are ex- 

 tended or contracted at the will of the animal, turned 

 in every direction, waved hither and thither and evi- 

 dently have the faculty of adhering very firmly by 

 their dilated tips to any object to which they are ap- 

 plied. 



So much we can discern as we watch the creature 

 disporting in this vessel of water; but we will now en- 

 deavour to learn a little more about its structure and 

 economy. Selecting for this purpose a sucher which is 

 extended to great length, I snip it across with a pair of 

 sharp scissors, as near the base as I can. Mark the re- 

 sult. The terminal knob which was attached to the 

 bottom of the saucer maintains its hold ; but the tube 



